Fixes webviews crashing on Eto.Gtk if the system only has webkit2gtk-4.1 installed instead of webkit2gtk-4.0. (4.1 is API compatible with 4.0, unlike 5.0 which currently hinders #2361)
Allows net6.0 as an alternative TFM for Eto.Gtk and Eto.Test and fixes the System.Range vs Eto.Forms.Range conflicts that arose from it.
This PR